Particle (proton and ion) beam radiotherapy holds the promise for improving cancer radiation treatment since it delivers energy in a better localized volume than X-ray (photon) therapy, owing to the Bragg peak of energy deposition near the end of an ion track. This increases the proportion of tumor cells to healthy cells that are damaged in radiation therapy. Current and future facilities require detectors to monitor the beam in real time for safety and to verify the dosimetry. This is especially true for facilities performing scanning beam therapy, since they can yield the best treatment results, using intensity modulated particle therapy, and highest patient throughputs but conversely need the best monitoring to ensure safety and proper dosage. We are developing a new scintillator-based detector for monitoring a scanning particle beam as it is used to irradiate the patient. This detector will track the position of the beam with millimeter and microsecond resolution in real-time in order to verify the beam position. In addition the detector will monitor the accumulated dose over a scan in order to validate the treatment. Using a scintillator means that the proton beam is minimally affected and no delicate components are exposed to the beam. The only component in the beam, the scintillator, is inherently robust and should show little aging due to the beam, and is inexpensive to replace, in any event. In Phase I, we tested several scintillators at the Francis H. Burr Proton Therapy Center at Mass. General Hospital (formerly called Northeast Proton Therapy Center or NPTC) and found two with the properties needed for a detector with the required position response, time response, and linearity. In Phase II, we will design and fabricate a working detector that is integrated into that treatment facility with the final scintillator chosen after additional measurements and design considerations. The design will provide the baseline detector that can easily be adapted to other proton and particle centers with some customization. A scanning particle beam facility requires a detector that performs like the one proposed. While many other elements go into a useful facility, this detector is a necessary item that helps produce improved radiation treatments for a wide variety of cancers. In addition to particle radiotherapy, the high resolution offered by robust, scintillator-based detectors also has application to photon radiotherapy. In particular, QA of IMRT treatment plans, which is currently time- consuming and difficult to perform with existing detectors, could be significantly improved using our technology. Part of our Phase II development will be devoted to this application, which can have significant impact on a radiotherapy modality that has a very large market. The proposed research will develop novel medical devices for radiotherapy, both for newer cancer radiation treatment facilities that use scanning particle beams and for more conventional facilities that use high-energy X-rays for IMRT. Intensity modulated radiation therapy requires better diagnostics in order to safely concentrate the radiation dose in the diseased tissue while sparing healthy tissue. The outcome of this research will enable therapists to deliver intensity modulated radiotherapy with greater confidence and patient safety and will also increase patient throughput and hence lower treatment costs. The net result will be improved cancer treatment for more patients. [unreadable] [unreadable] [unreadable]